Fluorescence X-ray techniques are widely used for elemental analysis. It offers an excellent sensitivity to trace elements down to picogram level. With the use of synchrotron X-ray sources, 3-D mapping of trace elements inside volumetric samples can be obtained with the so-called fluorescence X-ray computed tomography (XFCT) techniques [1]-[10]. In most of XFCT studies, a pencil-beam of synchrotron X-rays are used to scan through a volumetric sample from multiple view-angles, as shown in FIG. 1.a. Fluorescence X-rays, originated from the subvolume excited by the beam, are collected by a nonposition-sensitive x-ray spectrometer. 3D distribution of trace elements can be reconstructed from the measured line-integrals. As an alternative imaging scheme, confocal geometry has also been explored by many authors.
Chukalina et al. have reported an analytical evaluation of XCFT with a converging aperture system [11]. Woll et al. [12] and Vekemans et al. [13] have reported the use of polycapillary x-ray optics for confocal fluorescence x-ray microscopy. Similar to the line-by-line scanning scheme, these methods rely on scanning the focal-spot point-by-point through the volume (or surface)-of-interest to obtain a spatial mapping of trace elements. Despite the excellent imaging performances demonstrated in these studies, the need for mechanical scanning leads to long imaging times. In recent years, many efforts have been dedicated to improve the speed of XFCT studies [6], [7]. This is important for potential in vivo imaging applications as those reported by Takeda et al. [8]-[10]. The improved data acquisition speed allows for a greater throughput for XFCT studies with a limited beam time, which could make XFCT a more practical imaging modality for a wide range of applications.